1. Technical Field
The disclosure relates to an illumination device, and more particularly to an illumination device utilized with a light emitting diode (LED) light source.
2. Background
With the progress in semiconductor technology, the power attained by an LED becomes increasingly larger, and the intensity of the emitted light is getting even greater. In addition, the LED has the characteristics such as power saving, long lifetime, environment friendly, rapid response, small volume and the like. The LED is widely applied in the products including the illumination apparatus, the traffic lights, the displays, the optical mice, etc. for replacing the conventional fluorescent lamps or the incandescent bulbs. As for an LED bulb, several shortages are still existed. For instance, the direction of the light emitted from the LED per se is significantly anisotropic so that the light distribution of the LED bulb is not desirable.
Generally, the light distribution of the illumination apparatus can be represented by the beam angle thereof. FIG. 1 is a schematic diagram showing the measurement of the light distribution of the illumination apparatus. Referring to FIG. 1, the illumination apparatus L is placed in a dark room R and an illumination meter S measures the light emitted from the illumination apparatus L along the measuring trace T in the dark room R. A main light emitting direction A (the normal direction of the light emitting surface of the LED bulb) of the illumination apparatus L is defined as 0° and the measuring trace T is set to be located within the range of +150° to −150°. At this time, the illumination meter S is spaced from the illumination apparatus L at a distance d of 1 m, for example.
In a word, the measurement of the light distribution is performed by the illumination meter S spaced from the illumination apparatus L at a fixed distance d scanning along the range of +150° to −150° so as to obtain the light distribution curve of the illumination apparatus L. Herein, the angle range corresponding to where the illumination intensity is greater than half of the peak intensity in the light distribution curve can be served as the beam angle.
FIG. 2 is a schematic diagram showing the light distribution of an LED bulb in the related art. Referring to FIG. 2, the light distribution curve 10 shows the measured result of the LED bulb in the related art, wherein the illumination intensity measured at the angle range of +60° to −60° is greater than half of the peak intensity. Accordingly, it is noted that the beam angle of the LED bulb in the related art is about 120° based on the light distribution curve 10.